The present invention relates to a multi-mode valve. More particularly, the present invention relates to a multi-mode pressure relief valve for use in pressurized hot-melt adhesive systems.
Pressurized hot-melt adhesive systems are in use in a multitude of production facilities, in countless industries. For example, these system are used to seal cartons and containers for commercial products ranging from soda-pop to breakfast cereals to tools and consumables.
In pressurized hot-melt systems a pressure relief valve is provided to protect against failure of the equipment in the event of an abnormally high pressure situation. Typically this protection is provided by a mechanical pressure relief valve that vents high pressure to the tank or reservoir that supplies the adhesive.
It is also desirable to have the ability to quickly reduce the pressure within the system to a zero-pressure condition (known as zero-state). This is desirable for maintenance of the system, for emergency-stop situations, or the like. A mechanical pressure relief is not suitable for this purpose. As such, a separate pneumatic actuated valve is often provided for this function. Pneumatic operation allows the valve to be quickly deenergized to reduce system pressure. This, however, requires the use of a pneumatic circuit, actuator and other components.
Further, in some installations it is desirable to have the ability to adjust the adhesive pressure curve to match production speed requirements. This function maybe provided by a separate mechanical adhesive bypass valve, and/or by adjusting the pump speed dynamically with the parent machine line speed.
While this method functions well, often the adhesive pressure cannot be reduced quickly enough during a parent machine line stop. The result is excessive glue application on the final products.
As will be understood, each of these functions requires the use of a separate valve. These individual components each require maintenance, testing and the like in order to assure that they function properly. In addition, there is an initial capital cost associated with each. And, if a single component requires repair (or maintenance), it can adversely affect operation, not only of the adhesive system but of the parent line operation.
Accordingly, there is a need to reduce the number of components (valves) needed to carry out the pressure relief, zero-state and line speed following functions in a holt-melt adhesive application system. Desirably, such a valve has minimal moving parts. More desirably, such a valve is controlled by the pneumatic circuit of the adhesive system in which it is installed.